High quality medical remote imaging has gained increasing importance. This is particularly true of imaging during surgical procedures, most importantly minimally invasive procedures in which direct viewing of the surgical field is difficult. For example, a method for performing coronary artery bypass relies on viewing the cardiac region through a thoracoscope or other viewing scope (see for example Sterman et al. U.S. Pat. No. 5,452,733 and Gifford, III et al. U.S. Pat. No. 5,695,504). As a further example, a surgeon may perform a delicate vascular- or neuro-microsurgical reconstruction through a minimal incision under remote viewing. Remote imaging is now common in orthopedics, ophthalmology, urology, gynecology, anesthesiology, and other medical specifications.
In a conventional surgical environment, remote imaging is accomplished by attaching a video camera to an endoscope or other minimally invasive instrument and transmitting the video image via cable to a conventional CRT video monitor. This is often cumbersome in a crowded, brightly lighted operating room, where surgical team members are frequently moving around and the surgeon's view of the image screen is obstructed. Additionally, the CRT monitor is incapable of providing the surgeon with critical depth perception, since it is not stereographic.
Head-mounted displays (HMDs) potentially offer a method to overcome viewing obstructions typical in a surgical environment. While head-mounted displays have been designed, developed and deployed in military applications for many years, such displays are generally bulky, expensive, application-specific devices poorly suited to commercial or surgical applications. Additionally, users of head-mounted displays are frequently restricted in their range of motion by cumbersome interface cabling.
A compact HMD system requires a very small display device, such as those found in modern camcorder viewfinders, but with significantly higher resolution. A number of such devices are now becoming available, including transmissive and reflective liquid-crystal microdisplay devices and micro-mirror devices having resolutions at or in excess of VGA quality (640 pixels by 480 pixels) with pixel sizes on the order of 15 microns or less. However, they require integration into an ergonomic, well engineered and economical design. Most of these devices exhibit satisfactory image contrast only when illuminated and viewed at narrow angles of incidence, which compromises field of view, eye relief, and viewing comfort. Peripheral vision is also an important consideration.
A medical stereographic HMD system having dual display devices is described in Heacock et al. "Viewing Ocular Tissues with A Stereoscopic Endoscope Coupled to a Head Mounted Display (HMD)," http://www.hitl.washington.edu/publications/heacock/, Feb. 17, 1998. Kaiser Electro-Optics (2752 Loker Avenue West, Carlsbad, Calif. 92008 manufactures the "CardioView," "Series 8000," and "StereoSite" HMD display systems for Vista Medical Technologies. These systems are bulky, heavy, and expensive, and require two LCD display devices. For peripheral vision correction they require the user to wear the HMD over conventional corrective eyeglasses, aggravating user inconvenience and discomfort. Meyerhofer et al. U.S. Pat. No. 5,619,373, issued Apr. 8, 1997, describes a single display device involving beamsplitters for non-stereographic, biocular viewing.
The scan formats of video source devices, e.g., cameras and cassette players, are not directly compatible with typical solid state display devices. In particular, frame rates conforming with NTSC or PAL standards are too slow, and produce undesirable perceived flicker in solid state displays, which do not have the luminous persistence of phosphor screen displays, for example conventional TV displays. Therefore scan format and frame rate conversion are needed.
Heckman, U.S. Pat. No. 3,674,925, describes a wireless interface between a video camera source and a remote viewing display, employing a modulated optical video signal transmitter which doubles as a target illuminator. Hanson et al., U.S. Pat. No. 5,005,213, describes a wireless infrared/optical video interface directed to military applications. Puar et al., U.S. Pat. No. 5,650,955 describes an infrared interface for generating video images on a LCD or CRT display. However, the above cited U.S. Patents do not address, among other things, serial multiplexed color data, frame rate or scan format conversion.
Therefore, what is needed in the art is a compact, high resolution, high contrast microdisplay system, particularly for surgical viewing, that is suitable for head-mounted display use without requiring undue complexity or expense and that preferably supports biocular and/or truly stereographic viewing. The system should incorporate format and frame rate conversion to provide compatibility between solid state display devices and conventional video input sources. The system should provide good color fidelity and should incorporate ergonomic design for comfort and efficiency, including peripheral vision accommodation and minimal cabling.